1. Field of the Invention
The present invention relates to a liquid pump such as a water pump for forcibly circulating an engine cooling liquid such as water by means of a centrifugal force.
2. Description of the Prior Art
A conventional liquid pump of this kind is disclosed, for example, in Japanese Patent Publication No. 7(1995)-1037. This conventional water pump includes a body, a stationary member on which the body is fluid-tightly fixed through a seal member, a shaft which is rotatably supported on the body and an impeller which is fixed to one end of the shaft and which is disposed in a vortex chamber formed in the body. The impeller includes a disk portion which is fixedly fitted on the one end of the shaft at its inner circumference and plural blades which are formed on a side face of the disk portion directed toward the body so as to project toward the body and to extend radially. A stepped portion is formed on the body so as to be located adjacent to the vortex chamber. A partition plate having an inlet port is fixed on the stepped portion so that a predetermined axial clearance is maintained between the partition plate and end surfaces of the blades directed toward the body.
According to this prior pump, since the opening side of the blades directed toward the body is closed by the partition plate, a liquid from the inlet port is satisfactorily forced by centrifugal effects due to the rotation of the impeller. However, since the above prior pump requires the partition plate, the number of the parts not only increases but also a machining process of the stepped portion for fixing the partition plate to the body is required. Further, it is necessary to install the partition plate in addition to the installation of the seal member for assembling the liquid pump. As a result, in the above prior pump, the manufacturing cost of the pump is markedly increased. Further, in the above prior pump, an axial space for installing the partition plate is required and therefore the size of the pump is increased.
If a closing portion which closes the opening side of the blades of the impeller is formed on the impeller itself as disclosed in Japanese Utility-Model Application Laid-Open Publication No. 59(1984)-133798, it is possible tc overcome the above drawbacks. However, for this arrangement, it is difficult to manufacture the impeller having the closing portion and thereby the manufacturing cost of the pump is markedly increased.